1. Field of the Invention
This invention relates to a method of manufacturing a sheet metal poly-V pulley having a plurality of V-grooves arranged at a fixed pitch on the peripheral wall thereof from a sheet metal blank.
2. Prior Art
Since a poly-V pulley generally makes it necessary for a plurality of ridges formed on the poly-V belt to engage with V-grooves, the accuracy of each V-groove is vigorously demanded in the order of 5/100 mm. It is hence required that the pitch, width, and diameter of each V-groove be finished to close tolerances.
In an attempt to meet such demand, the applicant has already proposed a method of manufacturing a sheet metal made poly-V pulley in Japanese Patent Application No. 54-113820, wherein a plurality of V-grooves are formed on a cup-shaped blank by effecting rolling process by V-groove preliminary forming roller and compression process in the axial direction at the same time.
Said method is an improvement of a prior art proposed in U.S. Pat. No. 3,977,264, wherein a plurality of V-grooves are formed by folding a cup-shaped blank in the axial direction.
In other words, this is a method of forming specified poly-V grooves by pressing the peripheral wall of a cup-shaped blank formed from a sheet metal blank by deep drawing by means of a corrugating roller from the outer side thereof to corrugate the peripheral wall in a wavy section, compressing said cup-shaped blank in the axial direction while rotating with a V-groove preliminary forming roller movable in the axial direction being pressed to each bottom of the corrugated surface, and pressing a finishing roller to thus formed V-grooves while rotating the cup-shaped blank.
According to this method, therefore, as compared with the method proposed in said U.S. Publication, the pitch of poly-V grooves can be made uniform, and since the peripheral wall is not forcedly folded in the axial direction when forming V-grooves, the uneven biting which often occurs in the peripheral wall of cup-shaped blank conventionally may be eliminated. Moreover, since pattern-drawing or parting from the mold is easy, the manufacturing process may be simplified, defectives or non-conforming products may be reduced, and the sheet metal made poly-V pulley with improved quality can be presented.
However, in the case of this method, since it is required to fold by applying compression in the axial direction to the corrugated peripheral wall when forming V-grooves, uneven folds 9 were occasionally formed as shown in FIG. 17 in the V-grooves, and the wall thickness becomes thinner than the other parts in the poly-V groove 3 of a finished poly-V pulley product, thereby lowering the mechanical strength of the poly-V pulley, which has caused the inventor of this application to recognize the existence of further problems to be improved.